Pex18p

Pex18p is a peroxin (peroxisomal biogenesis factor) in the budding yeast Saccharomyces cerevisiae. It is encoded by the PEX18 gene and functions as a membrane-associated co-receptor in the peroxisomal import pathway.

Pex18p participates in the import of proteins containing a type 2 peroxisomal targeting signal (PTS2). The PTS2 receptor Pex7p binds PTS2-containing cargo in the cytosol, and Pex18p (along with Pex21p) helps anchor this receptor–cargo complex to the peroxisomal membrane and promotes its interaction with the docking and translocation machinery, including Pex13 and Pex14. This co-receptor system is distinct from the PTS1 pathway, which uses the Pex5p receptor.

Localization and interactions are central to Pex18p’s role. Pex18p is a peroxisomal membrane protein that interacts with Pex7p and Pex21p, forming part of the PTS2 import machinery. Through these interactions, Pex18p contributes to the proper docking of PTS2 cargo at the peroxisome and its subsequent translocation into the organelle.

Biological significance and genetic observations indicate that Pex18p is essential for efficient PTS2-dependent import in yeast. Loss or dysfunction of Pex18p disrupts PTS2 protein import and can affect peroxisome biogenesis and function, illustrating the importance of this co-receptor in maintaining peroxisomal protein distribution and organelle activity.

In summary, Pex18p is a yeast peroxisomal membrane co-receptor that collaborates with Pex7p and Pex21p to mediate the PTS2 import pathway, linking receptor recognition to the peroxisomal import machinery and contributing to peroxisome biogenesis and function.